Coiled blade assembly for belt scraper

ABSTRACT

The polyurethane scraping blade for a conveyor belt scraper is wound into a spiral coil around a spindle. End plates attached to the spindle have inward-facing flanges, which catch the edges of the coil, thereby preventing the coil from unwinding inadvertently. Even though the flanges keep the main body of the coil from unwinding, the free end of the coil is easily drawn from between the flanges.

This invention relates to belt scrapers, being belt scrapers of the kindused to scrape caked material from conveyor belts.

BACKGROUND TO THE INVENTION

Conveyor belts are in common use in mines, for the transport of ore toand from crushing, milling, and comminuting machines. Dust and fineparticles of crushed ore can become caked very firmly indeed to thebelt, especially if moisture is present.

Scraping caked material from mine conveyor belts is well-known to be amost demanding task. The task is usually approached on the basis ofpressing a scraper blade against the (moving) face of the belt. Thescraper blade gradually wears down under the abrasive conditions, andone of the problems of belt-scraping lies in providing a scraper bladeof sufficient length that the blade has a long service life betweenreplacements.

The conventional approach to the problem that the blade has only a shortlife is to press the blade against the belt with less force. Theinvention is aimed at providing an economical scraper in which the bladehas a long service life, yet in which the blade is pressed against thebelt with sufficient force for excellent scraping.

U.S. patent publication no U.S. Pat. No. 5,048,667 (MORIN, 17-Sep.-91)shows a scraper assembly in which the scraper blade is of flexibleplastic material, which is rolled into a coil. This arrangement has ledto a scraper assembly in which the scraper blade need only be changedon, say, an annual basis, as against the every-six-weeks replacementwhich has tended to be the industry standard in the most demandingsituations.

One of the problems that has arisen in regard to these coiled-bladescraper assemblies is that the blade can tend to stick or "freeze" tothe inside of the blade housing. As is shown in '667, the coiled bladeis contained inside a cylindrical housing. The inherent stiffness of theblade material means that the blade tends to try to unroll itself withinthe housing; in fact, the blade tends to uncoil itself until thematerial of the blade lies in direct touching contact with the inside ofthe housing.

Once the blade has unrolled itself as much as it can inside the housing,the friction of the blade material against the inside of the housingbuilds up, and this friction can make it difficult for the blade to moveand rotate within the housing.

If the blade is allowed to unroll inside the housing, ie if the blade isallowed to unroll itself and make frictional contact against the insidewall of the housing, the force required to drive the blade out of thehousing therefore increases; not only is the need for the increasedforce a disadvantage, but another disadvantage is that some of thecontrollability of the pressure of the blade against the belt is lost.

It may be noted that the friction is caused by the tendency of the beltto uncoil itself, rather than by the pressure forcing the blade againstthe belt.

In the said patent '667, the blade is driven out of the housing andagainst the belt by means of fluid pressure inside the housing. Onebenefit of this system is that the reaction to the belt contact force isnot supported by direct touching contact between the coil and thehousing, which eliminates a source of what would be a considerablefriction. However, the material of a scraper blade, even though able tobe wound into a coil, nevertheless is characterized as being very stiffand intractable; where the material does touch the housing as a resultof its trying to uncoil itself, the friction arising from that contactcan be considerable.

Thus, in '667, the blade is forced out of the housing in such a mannerthat the actuation force on the blade does not give rise to a frictionalresistance proportional thereto: the friction that arises simply due tothe tendency of the blade to uncoil itself inside the housing, is theproblem with which the invention is concerned. The problem existsbecause the coil of blade material tends to unwind itself until it comesinto contact with the housing, or with whatever is present that preventsit unwinding further.

The present invention is aimed at providing a scraper assembly of thecoiled-blade type, in which friction associated with contact between thecoiled blade and the blade housing is much less than has been the casein the previous scraper assemblies.

Another aim of the invention is to provide a scraper assembly in whichreplacement of the coiled blade is made more simple, by the fact thatthe replacement blade can be assembled in the factory into a coiled-upstate, and can remain so during insertion of the new blade into thehousing, whereby the service technician does not have to coil up theblade during or after assembly of the blade into the housing.

It is an aim of the invention to keep the blade material coiled tightlyenough that the coil cannot "escape" and start to touch the inside ofthe housing. On the other hand, it is an aim of the invention that theforce required to draw the free end of the blade out of the coil shouldbe a light force, and that the force should be as light when the coil isnew as when the coil is almost worn away.

It is an aim of the invention to keep the coil of blade materialconstrained against expansion without resorting to applying torque tothe coil. It would be theoretically possible, for example, to keep acoil tight by applying a torque to a spindle to which the inner end ofthe spiral coil is attached. However, it is preferred that the coil bekept under constraint by means which do not require a torque to beexerted between the coil and the housing: such a torque requirement, ifpresent, would greatly interfere with the freedom of choice of thedesigner to design an adequate actuator means for pressing the bladeagainst the belt.

It will be understood that if the constraint against unrolling were totake the form of a cage of some kind, placed so as to encircle the coil,the coil would simply unroll itself as much as possible within the cage.The friction of the partially unrolled coil against the cage then wouldbe hardly any less damaging than the friction of the partially unrolledcoil against the housing. Therefore, the means for constraining the coilagainst unrolling cannot, in practice, take the form of acoil-encircling cage.

It might be considered that it would be possible to position suitablemeans on the walls of the housing to hold the coil away from the walls,and to thereby stop the coil expanding. However, to avoid installationdifficulties, it is best for the coil containment constraints to beprovided, not by or from the housing, but in the coil assembly itself,ie in the assembly that is installed with the blade.

PRIOR ART

Apart from the above mentioned U.S. Pat. No. 5,048,667, coiled scraperblades are shown also in:

U.S. Pat. No. 4,877,122 (MORIN, 31-Oct.-1989)

U.S. Pat. No. 2,545,882 (HALL, 20-Mar.-1951)

FR-1378871 (MICHELIN, 12-Oct.-1964)

DE-AS-1051725 (ESCH-WK, 26-Feb.-1959).

GENERAL FEATURES OF THE INVENTION

The invention provides a means whereby the force with which a coiledscaper blade is pressed against the conveyor belt is rendered smoothlycontrollable. The invention provides a means for constraining the coilagainst unwinding, and consequent expansion and contact with the scraperhousing or other structure surrounding the coil.

Preferably, the means for constraining the coil against expansion iseffective to provide the constraint throughout the service life of theblade.

Preferably, the coiled blade assembly includes a spindle and two endplates, the coil being located between the end plates. The end platesare provided with axially-inwardly-extending, opposed flanges. Theflanges prevent the edges of the coil from unwinding and expanding.

It is recognised that because the blade is coiled into a tight cylinder,it is sufficient just to provide constraint at the very ends of thecoil. The wrapped coil is rigid enough that the middle part of the coil,though it might bow out slightly, will not bow out so much that the coilwould fall clear of the flanges.

It is recognised that the flanges therefore can be axially short. Thereis no need in fact for the anti-unwinding constraints to extend acrossthe full width of the blade. The fact that the blade is coiled into acylinder, and the fact that a coiled cylinder becomes a very rigidstructure, means that constraints placed only at the edges of the coilwill serve adequately. It is recognised that the flanges can be shortenough indeed that the free end of the blade can simply be pulled outfrom between the flanges.

Thus, the invention provides for just a light force to pull the free endof the blade out of the coil, and yet provides a very strong constraintto hold in the coil against its tendency to unwind.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of further explanation of the invention, exemplary embodiments ofthe invention will now be described with reference to the accompanyingdrawings, in which:

FIG. 1 is a pictorial view of a coiled scraper blade assembly, for abelt scraper;

FIG. 2 is a diagram of a factory set-up for coiling the scraper blade;

FIG. 3 is a front elevation, in cross-section, of the assembly of FIG.1;

FIG. 4 is an end elevation, in cross-section, of a belt scraper, inwhich the assembly of FIG. 1 is mounted for operational use;

FIG. 5 is a pictorial view of another coiled scraper blade assembly;

FIG. 6 is a front elevation of the assembly of FIG. 5;

FIG. 7 is a front elevation, in cross-section, of yet another coiledscraper blade assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The items shown in the accompanying drawings and described below areexamples which embody the invention. It should be noted that the scopeof the invention is defined by the accompanying claims, and notnecessarily by specific features of exemplary embodiments.

The scraper blade coil assembly 10 shown in FIG. 1 includes a length 12of scraper blade. The material of the blade is a hard polyurethaneplastic, or other suitable material. The blade material is typically 8mm thick, and may be, in a typical case, 120 cm wide. The width of theblade (ie the dimension measured along the axis of the coil) is set tobe a little less than the width of the belt it is to scrape. (The bladeshould be the same width as the belt except for a margin of tolerance toensure the edges of the blade cannot overhang the edges of the belt.)The length of the blade, ie the dimension which is to be coiled, in atypical case may be two or three meters.

Such a blade is flexible, in that it is possible to bend the materialinto a coil. However, the force required to bend the material isconsiderable; it will be understood that such a blade is flexible enoughthat the blade might be bent by hand, but the blade is so stiff as tomake the coiling of the blade, and the retention of the curvaturetherein, a task which cannot, in practice, be done manually.

The blade 12 is gripped between two end plates 14, 16. A spindle 18connects the end plates.

FIG. 2 illustrates the manner in which the blade is coiled. In thefactory (ie not at the scraper site), belt material 20 is fed through apair of pinch rollers 23. The spindle 18 is mounted in suitablebearings, and the free end of the belt material is clamped between aclamp face 25 of the spindle and a clamp bar 27. Clamp bolts 29 passthough the clamp bar 27 and through holes in the blade material 20.

In the factory where the coil assemblies are prepared, the spindle 18 isso mounted in the bearings that the spindle may be forcefully rotated,whereby the belt 20 is drawn through the pinch rollers 23, and becomescoiled around the spindle. The pinch rollers are set to resistpull-through forces, to the extent that the tightness of the coil 30 ofthe belt material is controlled by the resistance to rotation of therollers 23.

After the required length of material has been wound into the coil 30,steps are taken to ensure that the coil cannot now unwind itself. (Thetendency of the coil to unwind itself is inherently present at alltimes.) This might be done for example by maintaining a torque on thespindle 18, and locking the rollers 23, or it might be done by placingrestraints 32 around the circumference of the coil 30.

Now, with the coil restrained against unwinding, the end plates 14, 16are tightened onto the ends of the spindle 18. The end plates aretightened (in the axial direction) towards the edges of the bladematerial 20 coiled about the spindle. The application of the end platesonto the spindle is made easier if the ends of the spindle are free, ieif the spindle has been removed from any torque applicators or bearingsin which it was mounted during coiling.

With the end plates 14, 16 in place, the blade material 20 is cut tolength. The restraints 32 may now be removed, and the assembly is readyfor operational use. The end plates serve to keep the coil fromunwinding, as will explained below. For storage and handling prior touse, a band may be placed circumferentially around the coil to preventunwinding in case of accidents.

The end plates 14, 16 are tightened against shoulders 34 provided on thespindle 18. Studs 38 extend outwards from the spindle, and pass througha suitable through-drilling in the centre of the end plate. Each endplate is secured in place over the respective stud by means of a nut 39.

Means are provided for preventing the end plates 14, 16 separating fromeach other, and from moving axially outwards with respect to the spindle18. To inhibit the nut 39 from working loose, the designer may arrangethat each end plate is secured against rotation relative to the spindle,for example by means of a tongue on the hub of the spindle, whichengages a suitable groove on the shoulder 34. Or, the designer mayarrange that the nuts are locked to the studs.

The designer may choose to make the end plates free to rotate on thespindle, or may choose to secure the end plates against rotation. InFIG. 3, the end plates are secured against moving axially relative tothe spindle, and are secured against rotation.

The end plates are provided with respective opposing flanges 40, whichprotrude axially inwardly. As shown in FIG. 3, the axial width 43 of theblade material is greater than the distance apart 45 of theinward-facing surfaces 47 of the flanges 40.

It will be appreciated that, in order for the material to pass betweenthe flanges, the material must be curled in the manner as shown in FIG.1 in relation to the free end 49 of the blade.

Apart from the flanges 40, the rest of the end plates need not be sotight on the blade material as to compress the material, although aslight pinch can be accommodated. The designer must see to it that theend plates are so shaped and mounted that the blade material cannotescape from between the flanges; if the end plates were allowed toseparate, the coil would cease to be constrained by the flanges, andwould uncoil itself.

In the assembly as shown, the cylindrical coil of blade material iscontained between the end plates, and is restrained from expansionbeyond a predetermined diameter by the presence of the flanges 40. Thecoil may be expected to uncoil and expand itself fully to the extentpermitted by the flanges.

FIG. 4 shows the scraper blade assembly 10 fitted inside the housing 50of a belt scraper. The housing is supplied with a fluid (eg water) whichpressurises the interior chamber 52 inside the housing, and urges theblade out of the housing, and into contact with the moving belt 54 whichis to be scraped. The blade passes out of a slot 56 in the housing 50,in which the blade is sealed to the housing by means of an elastomericseal. In some designs of scraper, the chamber 52 is pressurised all thetime during operation of the scraper; in other designs, the housing ispressurised only intermittently during operation. In still otherdesigns, the chamber is not pressurised, but rather the coiled blade isforced out of the housing by a different type of means, for example bythe use of mechanically biassed grip-rollers.

The housing 50 is basically cylindrical in shape, and is fitted with adetachable end cover (not shown), through which the blade assembly 10can be inserted. The service technician removes from the assembly 10 thetransport safety band, if fitted, just prior to inserting the assemblyinto the housing. The technician feeds the free end 49 of the coiledblade up through the slot 56.

There is no connection between the coil assembly 10 and the housing 50other than at the sealed slot 56. There is no requirement for thespindle 18 to be physically attached to the end cover of the housing,for instance. The assembly 10 simply rests inside the chamber 52.

As the blade material 12 is drawn from the coil 30, the coil rotatesinside the housing 50. Thus if the coil includes say eight turns ofblade material, the coil, and the spindle 18, end plates 14, 16, etc,undergo eight rotations within the housing during the service life ofthe blade. (Actually, the number of rotations of the spindle would beless than that, because the coil continually unwinds to the maximumdiameter as the blade is drawn off.) As mentioned, the coil assemblysimply rests inside the housing: no bearings or the like are required tocater for this rotation.

It will be understood that there is no need for the technician, whenfitting the coil assembly into the housing, to apply forces to theassembly by way of coiling up the blade. The only force the technicianis required to exert is that of lifting the assembly into place.Inevitably, because of restricted access, this lifting will have to becarried out by physically manhandling the assembly. But the assembly 10is light in weight: the plastic blade material is not heavy, and thespindle, end plates, and other components can be made of aluminum in thebigger sizes of scraper where weight might start to be a problem.Alternatively, the flange may be a plastic moulding, and the spindlecomponents may be of stainless steel. For removing a worn out blade, ofcourse only a short length of the blade material will still be present.

As mentioned, the blade material 12, though rolled into the coil asdescribed, is stiff, and must be kept under tight control to prevent itsunrolling. If the coil is allowed to unroll itself, the blade materialwill contact the inside of the housing 50, and may "freeze" to thehousing. Whilst the coil can be permitted to unwind to some extent, thecoil must be constrained against unwinding itself so much that the coilfills the width of the chamber.

In the design as shown, the blade material is wider, as at 43, than thedistance apart 45 of the flanges 40. In the housing 50, duringoperation, the coil 30 expands, ie unwinds itself, until the axial endsof the blade material contact the radially-inside-facing surfaces 60 ofthe flanges. The only way for the blade material to be released frombetween the flanges is if the free end 49 of the blade is buckledslightly to a curve, as shown in FIG. 1. When this happens, the bladecan be withdrawn from between the flanged end plates. In fact, when thefree end is allowed to buckle in this manner, the free end can be drawnfrom the coil with little force.

It might be considered that, if it is indeed easy for the blade materialto buckle, and pass between the flanged end-plates, that the blade mightsimply buckle all at once, and thus fall out from between the endplates. The answer lies in the different curvatures of the blade. At thefree end of the blade material, the material can buckle because thecurvature of the blade about an axis lying parallel to the axis of thespindle is practically zero once the blade has left the coil. But in themain body of the coil, the blade material is tightly curved to acylindrical radius about the spindle axis. It requires little force tomake the blade material buckle once the blade material has left thecoil: it would take a huge increase in force to make the blade materialbuckle while the blade material is still in the coil, and still curvedinto a tight cylinder.

Thus, in the main body of the coil 30, the blade material remainsright-cylindrical. As explained, the coil has a large inherent tendencyto uncoil itself as much as it can within the confines of the flangedend plates 14,16; but the coil displays very little tendency to bulgeand buckle, in the central portion of the coil, between the end plates.This is not to say that the cylinder of the coil remains perfectlyparallel-edged: certainly the cylinder of the coil will go slightlybarrel-shaped, especially if the blade is wide. But it is recognisedthat there is only a tiny chance (it cannot be said there is nopossibility whatsoever) of the coil bowing or barrelling out in themiddle to such an extent that the coil could free itself of the flangedend plates.

Even though the main body of the coil is firmly held by the geometry ofits cylindrically-coiled curvature, the fact is that once the bladepasses out of the coil, and the coil-curvature disappears, the bladebuckles quite easily. Therefore, the force required to pull the free end49 of the blade material out from between the end plates is really quitesmall. Furthermore, the force required to pull the blade clear, remainsmore or less constant throughout the whole length of the coil, ie theforce required to pull the free end of the blade out from between theend plates is the same whether the blade is new and unworn, or whetheronly a few cm of blade material remain.

It may be considered that the edges of the blade might be damaged bybeing dragged through the flanges. However, no difficulties arise here:firstly, if the edges of the blade were damaged it would not matterbecause the edges of the belt are usually the least demanding as regardsscraping; but in any event it turns out that virtually no chewing-up ofthe edges of the blade can be perceived.

The performance of the device as illustrated may be summarised asfollows. A flexible material, when formed into a relatively tightcylindrical coil, greatly resists barrelling. However, once the materialis clear of the cylindrical coil, the material can buckle into the kindof curve shown in FIG. 1 with little resistance. In the assembly asshown, the coil unwinds itself progressively as more blade material isdrawn off, so that the coil is always tight against the insides 60 ofthe flanges. But the blade material can be pulled clear of the flangeswith only a light force, which remains light even when the coil is(almost) completely unwound.

In fact, as the blade material becomes nearly completely worn away, theproblem of the blade material coil expanding and freezing against thehousing walls tends to disappear. It is only when the coil includesenough material to form at least one area of overlap between adjacentturns of the coil that the problem of the coil freezing to the housingis substantial. Another preferred manner in which the scraper bladematerial may be wound into a coil will now be described.

In the previously described design (FIGS. 1-4), the blade is wound intoa coil as a factory operation; the coiled blade, as shown in FIG. 1,constitutes the product that is made in the factory and sold as areplacement blade (or indeed as an Original Equipment blade). To fit thereplacement blade, the user opens up the axial ends of the housing, andinserts the already-coiled "cassette" (ie the assembly shown in FIG. 1)into the housing. The technician then manoeuvres the free end of theblade out through the slot 56.

In some cases, there can be a difficulty in registering the free end ofthe blade with the slot 56 from the inside, especially since there is noroom for the technician to pass his hands into or inside the housing 50when the coil 30 is present in the housing.

It is often preferred therefore to insert a replacement blade fromoutside the housing. FIGS. 5-6 illustrate a system in which thispreference is accommodated.

In FIG. 5, the blade 64 is formed on what will be the inner end of thecoil of the blade material, with a tongue 65. The tongue 65 has twoslotted holes 67. A spindle piece 69 is provided with two pegs 70, whichengage the holes 67.

It will be understood that the task of attaching the tongue to thespindle piece is carried out from inside the housing 50. The tongue 65is inserted through the slot 56 from outside the housing, while thelength of the blade 64 is disposed outside the housing, and then thespindle piece is assembled to the tongue 65.

With the tongue 65 assembled to the spindle piece 69, a backing piece 72is fitted also over the pegs 70. Then, square tubular sleeves 74 areplaced over the ends of the spindle piece and the backing piece. Theends of these pieces are chamfered, to enable the sleeves to slideeasily onto the pieces. It will be noted that these operations caneasily be carried out, by hand, by the technician working with his handsinside the housing. No tools are required, and no heavy forces need beexerted.

With the sleeves 74 in place, screwed rods 76, which are integral withthe spindle piece 69, protrude axially from inside the sleeves. Thetechnician now places one of the end plates 14 over one of the screwedrods 76, and tightens the end plate in place with a nut 78. Thetechnician carries out this task with the assistance of a wrench orspanner of suitable form.

The technician now continues to turn the nut 78, thereby rotating thespindle 69. This action coils the blade material 64 around the spindle69. The technician continues to rotate the spindle until all the lengthof the blade 64 is coiled around the spindle, except for a small marginof the blade, which he leaves still protruding out of the slot in thehousing. The technician places a clamp on this protruding margin, toprevent it from being drawn in through the slot, and then he may tightenand straighten the coil, and position the coil correctly in the housing.The technician also at this time places the other end cap 16 onto theother of the screwed rods 76, and assembles a nut to hold same in place.

The technician tightens the nuts, drawing the two flanges together,until the coil is positioned (axially) centrally between the two endcaps. The holes 67, being slotted, permit a certain degree of axialshuffling of the coil along the spindle. The end plates are nottightened onto the ends of the coil so as to compress the coil, but onlyso as to lightly touch the ends of the coil. When the nuts 78 arecorrectly tightened, locknuts may be placed on the screwed rods 76 toprevent backing off.

The above-described operations on the nuts can be carried out with thecoil components residing inside the housing, since the only accessrequired is to the nuts and the screwed rods.

The system described with reference to FIGS. 1-4 provides a pre-coiledblade assembly, which is fitted as a cassette into the housing. Theouter end of the coil is fed through the slot in the housing from theinside. In the FIG. 5-6 system, by contrast, the replacement blade iscoiled into the housing by an on-site technician, who inserts a tongueof the blade into the housing from outside. In FIGS. 5-6, the extrainconvenience of having to carry out the on-site operations of attachingthe blade to the spindle, and of having to coil the blade around thespindle, is offset by the extra convenience that arises from insertingthe new blade from outside.

One of the difficulties facing the designer of the assemblies asdescribed herein is the fact that the polyurethane as used for the bladematerial has a high coefficient of thermal expansion. If the scraper isto be installed in a place which suffers extremes of temperature, theblade material can undergo a dimensional change, across the width of thecoil, of 3 or 4 mm, from cold winter nights to hot summer sun.

The designer must see to it that the blade does not contract during coldweather so much that the blade material pops out from between theflanges on the end-plates.

In FIG. 3, the end-plates 14, 16 are tightened against shoulders 34 onthe spindle 18. This arrangement does not practically allow forcontraction. In FIG. 6, the end plates are tightened against the coil ofblade material; in this arrangement, the coil can be compressed axiallybetween the end-plates. The designer then can specify that 3 mm or otherappropriate amount of pre-compression be built in (when the componentsare assembled at room temperature) that even the coldest temperaturewill not cause sufficient contraction that the coil breaks contact withthe end plates.

In FIG. 7, the end-plates 80 are slidable along the spindle 83. Theend-plates are forced into contact with the ends of the coil 85 by meansof springs 87. If the coil should expand/contract axially, theend-plates can follow the movement, and the springs 87 keep the contactforce more or less constant.

It is usually convenient to arrange that the end-plates cannot rotaterelative to the spindle. To this end, an extension component 89 of thespindle is of hexagonal shape, and the end-plates are provided withcomplementary hexagonal holes, whereby the end-plate can slide along thespindle, but cannot rotate relative thereto.

I claim:
 1. Coiled blade assembly for a conveyer belt scraper,characterised in that:the assembly includes a blade (20) of scrapermaterial, the blade being suitable for pressing against the belt, andfor scraping and cleaning the belt; in the assembly, the blade materialis arranged in a spiral coil (30) of more than one turn, about a coilaxis, the coil having left and right axial ends; the assembly includesleft and right coil-constrainers (14,16), which are arranged so as toconstrain the coil against radial expansion; the assembly includesstructure (18) for holding the left and right coil-constrainers inposition at, or near, the respective axial ends of the coil; thecoil-constrainers extend a distance in from the ends of the coil; thedistance is long enough that the coil is substantially firmlyconstrained by the coil-constrainers against radial expansion, at leastduring operation of the scraper; the distance is short enough that,during operation of the scraper, an outer end (49) of the blade materialforming the coil can be drawn smoothly and freely from the coil, betweenthe coil-constrainers.
 2. Assembly of claim 1, wherein the left andright coil-constrainers respectively comprise left and right rings thatencircle the coil at, or near, the ends thereof.
 3. Assembly of claim 1,wherein the structure for holding the left and right coil-constrainersin position comprises a means which is effective, if the coil shouldtend to thermally expand/contract as to its axial dimension duringoperation, still to hold the coil-constrainers in position at, or near,the respective axial ends of the coil during that expansion/contraction.4. Assembly of claim 1, wherein:the assembly includes left and rightend-plates, positioned respectively at the left and right ends of thecoil; the coil-constrainers comprise axially-inwardly-extending flangesof the end-plates.
 5. Assembly of claim 4, wherein the assembly includesstructure for holding the left and right end-plates against therespective ends of the coil.
 6. Assembly of claim 5, wherein thestructure for holding the left and right end-plates against the ends ofthe coil is effective, during operation, to constrain the end-platesagainst relative separation thereof, in the axial sense.
 7. Assembly ofclaim 6, wherein the structure for holding the left and right end-platesagainst the respective ends of the coil is arranged, prior to operation,to pre-compress the coil in an axial sense by an amount, where theamount is more than the axial thermal contraction of the coil occasionedby a reduction in temperature of the assembly during operation. 8.Assembly of claim 5, wherein the structure for holding the left-andright end-plates against the respective ends of the coil is effective topermit the end-plates to move axially relative to each other, andthereby to follow such thermal expansion/contraction movement of thecoil as may occur in the axial sense during operation.
 9. Assembly ofclaim 8, wherein the structure for holding the left and right end-platesagainst the respective ends of the coil includes a resilient means,which is effective to keep the force of the end-plates against the endsof the coil substantially constant as the end-plates undergo suchmovement.
 10. Assembly of claim 4, wherein the end-plates are lockedagainst rotation relative to the spindle, whereby, as the coil rotatesand unwinds, the coil, spindle, and end-plates rotate as a unitarywhole.
 11. Assembly of claim 1, wherein the distance is about 3 mm. 12.Assembly of claim 1, wherein the coil-constrainers are effective toconstrain the coil against expansion during transport and storage of thecoil, away from the belt.
 13. Coiled blade assembly for a conveyor beltscraper, in structural combination with a housing of the said scraper,characterised in that:the conveyor belt scraper is of the kind in whichthe coiled blade assembly is, during operation of the scraper, housed inan interior chamber of the housing (50), walls of the chamber definingan internal clear space of sufficient diametral width to accommodate theassembly; the assembly includes a blade of scraper material, the bladebeing suitable for pressing against the belt, and for scraping andcleaning the belt; the combination includes a mounting means, on whichthe blade is mounted, and on which the blade is arranged in a spiralcoil of more than one turn, about a coil axis; the arrangement of theassembly is such that, when the assembly is present in the housing, afree end of the coiled blade is available to pass out through thehousing and into scraping contact with the belt; the combinationincludes a coil constraining means, which is effective, during operationof the scraper, to prevent the coil from unwinding and expanding inwidth beyond a predetermined diametral constraint width; and the saidpredetermined diametral width to which the coil is constrained is lessthan the diametral width of the housing chamber, whereby the coil isconstrained against unwinding and expanding into contact with the wallsof the chamber.
 14. Combination of claim 13, wherein the arrangement ofthe coil constraining means is such that the means is effective to soprevent the coil from unwinding beyond the said constraint widthsubstantially throughout the whole operational service life of theblade.
 15. Combination of claim 13, wherein the coil constraining meansis integral with the assembly, in that the means is effective to soprevent the coil from unwinding both when the assembly is physicallyseparate from the housing, and when the assembly is present inside thehousing.
 16. Assembly of claim 5, wherein the said structure extendsinside the coil along its axis.